Spalling is essentially the effect of turning the interior of an armored vehicle into anti-personnel projectiles. Even if a vehicle’s armor plate is thick and dense enough to prevent penetration, adequate compression and shock waves can cause the interior of the armor plate to fragment and splinter potentially injuring/killing the crew. US anti-armor rounds consist generally of kinetic (sabot) and chemical (HEAT) rounds for which spalling is largely a secondary effect. The British make extensive use of the HESH round for which spalling is its primary effect.